Depending on the criteria, WW2 was well underway when the USSR "annexed" the Baltic States in 1940, Some would say WW2 started in 1931 when Japan invaded Mukden in northeastern China. Others include the Spanish Civil War from 1936. Of course, the Brits consider September 1939 as the beginning. All depends on your criteria and point of view, I guess.
Others say 2nd Sino-Japanese war, i.e. 1937.
Like I said, depends on where you stand.